1. Field of the Invention
The present invention relates to an electric energy storage device and a method for manufacturing the same, more particularly, to an electric energy storage device including a gel type ionic conducting polymer electrolyte separator which enhances storage capacitance and reduces resistance, and a manufacturing method thereof
2. Description of the Related Art
Capacitors are generally classified into three categories: electrostatic capacitors, electrochemical capacitors and electrolytic capacitors. The electrostatic capacitors include a ceramic capacitor, a glass capacitor and a mica capacitor. The storage capacitance of the electrostatic capacitor is between approximately 1.0 xcexcF and 10 xcexcF.
The electrochemical capacitors are called supercapacitors. The electrochemical capacitors include an Electric Double Layer Capacitor (EDLC), a metal oxide pseudocapacitor and a conducting polymer capacitor. The storage capacitance of the electochemical capacitors is between approximately 1 mF and 3,000 F.
Some capacitors such as an aluminum electrolytic capacitor and a tantalum electrolytic capacitor are types of the electrolytic capacitors. The storage capacitance of the electrolytic capacitor is normally hundreds of times larger than that of the electrostatic capacitor.
In general, an electrode of the electrolytic capacitor is made by etching a valve metal, such as aluminum (Al), and by carrying out a chemical process or an electrochemical process. An electrode of the electrolyte capacitor is manufactured by sintering a valve metal powder, such as an aluminum powder or a tantalum powder, to have a large specific surface area. Then, the electrode is immersed in an electrolyte to form the electrolytic capacitor.
FIG. 1 is a cross-sectional view of an electrolytic capacitor according to a related art. Referring to FIG. 1, an electrolytic capacitor of the related art is comprised of a cathode 10 which includes a valve metal and an oxide layer 5, an anode 15 corresponding to the cathode 10, a separator 20 between the cathode 10 and the anode 15, an electrolyte (not shown) injected into the separator 20, terminals 11 and 16 respectively attached to the cathode 10 and the anode 15, and a case for sealing the cathode 10, the anode 15 and the separator 20.
The oxide layer 5 is formed on the valve metal which is formed by etching a foil or sintering a metal powder. The oxide layer 5 is generally composed of an aluminum oxide (Al2O3) or tantalum oxide (Ta2O5) made by the electrochemical method.
The separator 20 between the anode 15 and the cathode 10 has an ionic conductivity. It also insulates the anode 15 from the cathode 10. The electrolyte is permeated into the anode 15 and the cathode 10, which stores the charge and provides a conducting medium for the ions.
The electrolytic capacitor is widely applied to various electronic devices because of its large storage capacitance, low resistance and low manufacturing cost. Yet, the size and the resistance of the electrolytic capacitor need to be further reduced given the recent development of various electronic devices such as notebook computers and cellular phones.
Considering the need for reducing resistance and minimizing the size of the electrolytic capacitor, a solid electrolytic capacitor, including an electronic conducting material which is injected into cathode, will likely be in demand. The electronic conducting material is composed of manganese oxide (MnO2), tetracyanoquinodimethane (TCNQ) or polypyrrole (PPY).
However, the electrolytic capacitor of the related art has some disadvantages which are described hereinbelow.
FIG. 2 is a perspective view of an electrolytic capacitor having a cylindrical shape according to a related art. Referring to FIG. 2, the electrolytic capacitor of the related art is comprised of a cathode 35, an anode 45, first and second separators 30 and 40, respectively attached to the cathode 35 and the anode 45. The electrodes 35 and 45 and the separators 30 and 40 are wound together to form the electrolytic capacitor. The resistance or the size of such electrolytic capacitor, however, is not easily reduced through the manufacturing process of the electrolytic capacitor.
An electrolytic capacitor includes either a solid electrolyte such as a tantalum electrolytic capacitor or an aluminum PPY electrolytic capacitor, or a liquid electrolyte. In case of using a solid electrolyte, the capacitor generally consists of an anode, and an electronic conducting electrolyte as cathode and terminals. On the other hand, in case of using a liquid electrolyte, the capacitor consists of an anode, a cathode, a separator and terminals.
As for the electrolytic capacitor including the electronic conducting solid electrolyte, a thin layer of cathode is formed on the anode after the anode has been manufactured by etching a metal foil or sintering the metal powder, followed by the formation of an oxide layer on the etched foil or the sintered powder.
In the electrolytic capacitor including the ionic conducting liquid, the cathode, the separator and the anode are approximately 0.05 mm, 0.05 mm and 0.1 mm thick, respectively. That means that the electrolytic capacitor including the liquid electrolyte is much thicker than the electrolytic capacitor including the solid electrolyte. In addition, a liquid electrolyte of the electrolytic capacitor generally has low ionic conductivity.
Hence, the electrolytic capacitor including the ionic conducting liquid electrolyte has more resistance than that of the electrolytic capacitor including the electronic conducting solid electrolyte, since the thickness of the separator needs to be at least approximately 0.05 mm in order to prevent the separator from being torn and the conductivity of the liquid electrolyte is much lower than that of the electronic conducting solid electrolyte.
Considering the above-described problems and disadvantages, it is an object of the present invention to provide an electrolytic capacitor including a liquid electrolyte, which has a low resistance and a large storage capacitance, and a manufacturing method thereof.
It is another object of the present invention to provide a manufacturing method for an electric energy storage device using wound electrodes with a gel type ionic conducting polymer electrolyte separator to increase productivity and yield.
To achieve the above objects, the present invention provides an electrolytic capacitor including an ionic conducting polymer electrolyte separator composed of common solvent and polymer. The common solvent functions as an electrolyte as well as a dissolvent of the polymer. The polymer is composed of at least one selected from the polymer groups of polymer of polyacrylate series, polyvinylidenefluoride (PVdF), copolymer of polyvinylidenefluoride and polymer of polyether series.
According to one example of the present invention, a common solvent is composed of propylene carbonate (PC) including alkylammonium compounds such as tetraethylammoniumtetrafluoroborate (Et4NBF4) or amide compounds such as tertiary amide. In this case, the polymer is composed of polyacrylonitrile (PAN) and polyvinylidenefluoride, wherein the weight ratio between the polyacrylonitrile and the polyvinylidenefluoride is approximately 1:1 to 5:1. However, the preferred weight ratio between the common solvent and the polymer is approximately 4:1 to 10:1.
In another example of the present invention, the polymer is composed of polymethylmethacrylate (PMMA) and polyacrylonitrile. In this case, the weight ratio between the polymethylmethacrylate and the polyacrylonitrile is approximately 1:1 to 4:1.
According to still another example of the present invention, the common solvent is composed of gamma-butyrolactone ((xcex3-BL) including alkylammonium compounds such as tetraethylammoniumtetrafluoroborate or amide compounds such as tertiary amide. The polymer is composed of polyacrylonitrile and the weight ratio between the common solvent and the polymer is approximately 5:1 to 8:1.
In still another example of the present invention, the common solvent is composed of propylene carbonate and gamma-butyrolactone including alkylammonium compounds, such as tetraethylammoniumtetrafluoroborate or amide compounds, such as tertiary amide. In this case, the amount of the propylene carbonate is more than that of the gamma-butyrolactone and the polymer is composed of polyacrylonitrile and polyvinylidenefluoride or polyethylene oxide.
Also, in order to achieve the above objects of the present invention, the electrolytic capacitor of the present invention further includes a first electrode on which the separator is formed and a second electrode corresponding to the first electrode, wherein the separator, the first electrode and the second electrode are wound together. Preferably, the first electrode is a cathode.
According to one embodiment of the present invention, a first electrode which has a larger width than the second electrode, is longer than the second electrode.
According to another embodiment of the present invention, an isolating member is formed at the end portion of the first electrode or a portion of the second electrode where the end portion of the first electrode is positioned. The isolating member is composed of a tape or a paper.
In addition, the electrolytic capacitor of the present invention has an additional electrolyte which is injected into the first and second electrode. It is identical to the common solvent of the separator or different from the common solvent of the separator, thereby enhancing the performance of the electrolytic capacitor and reducing the manufacturing cost of the electrolytic capacitor.
To achieve the above objects of the present invention, the present invention provides an electric energy storage device having an ionic conducting electrolyte, including a gel type ionic conducting polymer electrolyte separator, a first electrode on which the separator is formed, and a second electrode corresponding to the first electrode, wherein the separator, the first electrode and the second electrode are wound together.
Also, to achieve the above objects of the present invention, the present invention provides a method for manufacturing an electric energy storage device including the steps of: forming an ionic conducting polymer electrolyte separator including i) preparing common solvent for an electrolyte and for dissolving polymer and ii) dissolving the polymer at least one selected from the group consisting of polymer of polyacrylate series, polyvinylidenefluoride, copolymer of polyvinylidenefluoride and polymer of polyether series in the common solvent. The step of forming the separator may further includes a step of heating a mixture of the common solvent and polymer, and a step of coating the mixture on a current collector.
According to the present invention, the electrolytic capacitor has an increased unit storage capacitance with minimized size by using the gel type ionic conducting polymer electrolyte separator. Also, the resistance of the electrolytic capacitor is reduced by using the gel type ionic conducting polymer electrolyte separator. Consequently, the electrolytic capacitor of the present invention enables enhancement of a high frequency response characteristic, enlargement of the available frequency region and increase of the allowable ripple current of the electrolytic capacitor.